Senior Lecturer The University of Queensland Brisbane, Queensland, Australia
Background/Question/Methods
Understanding how ecological communities assemble has been a central topic in ecology. Community assembly can be affected by two types of rapid evolution with species interactions: evolution-mediated priority effects (EPE) and ecological character displacement (ECD). In EPE, species that arrive early prevent colonization of late-arriving species via local adaptation (i.e., community monopolization via niche preemption). On the other hand, ECD promotes species coexistence by niche partitioning. The two processes have been discussed separately, and it is unclear which process becomes dominant in community assembly under various conditions. Here, we developed a theoretical framework to synthesize and compare the two processes. We constructed and analyzed mathematical models of two species competing for common resources (i.e., the discrete-time Leslie-Gower competition model, the continuous-time Lotka-Volterra competition model, and the MacArthur’s consumer-resource model) with eco-evolutionary feedbacks. We assumed a trade-off between the intrinsic growth rate and interspecific competition: species can increase its intrinsic growth rate through convergence to the optimum trait value, but it intensifies interspecific competition. For simplicity, we assumed that a late-arriving species does not evolve due to, for example, rare but repeated immigration events from a regional species pool.
Results/Conclusions
When interspecific competition can become stronger than intraspecific competition, we found that there are alternative stable states (i.e., two locally stable equilibria) in the two-species eco-evolutionary dynamics. One equilibrium is coexistence with niche partitioning and the other one is competitive exclusion through maximization of the intrinsic growth rate of an evolving species. In simulations of community assembly dynamics, we revealed that the difference of immigration timing between an early-arriving species and a late-arriving species can be a key parameter. When the difference of immigration timing is small, ECD occurs because insufficient local adaptation of the early-arriving species allows colonization of the late-arriving species. When the difference is large, on the other hand, EPE arise because niche preemption by local adaptation of the early-arriving species causes competitive exclusion of the late-arriving species. In conclusion, our research suggests that the difference of immigration timing between two species can be significant for determining the relative importance of ECD and EPE in community assembly.
